"you can't drive a unipolar motor with a bipolar driver. its to do with the fact that current flows in both directions in the bipolar motors and only one direction in the unipolar. hence the names."
This is not completely true, you can drive 6 and 8 wire unipolar motors with a bipolar driver by ignoring the centre tap and using the 2 coils on each in series to effectively create 1 coil a side.
See the attachment to my first post and I have since found another article confirming this and also confirming 5 wire motors cannot be driven by a bipolar driver.
http://schmalzhaus.com/EasyDriver/
Neale